This subproject is one of many research subprojects utilizing the resources provided by a Center grant funded by NIH/NCRR. The subproject and investigator (PI) may have received primary funding from another NIH source, and thus could be represented in other CRISP entries. The institution listed is for the Center, which is not necessarily the institution for the investigator. A virtually universal property of viruses is the requirement for the virus coat to make the transition from being an inert rigid protective outer coating to an activated dynamic particle capable of nucleic acid delivery during infection. This dynamic process requires conformational changes in the virus coat (Poranen, Daugelavicius, and Bamford, 2002) (Dryden et al., 1993;Endrich, Gehrig, and Gehrig, 1999;Fuller and Lee, 1992;Kirnbauer et al., 1993). However few mechanistic details are available about this essential process because of a lack of a model research system, an easily detectable phenotype and an assay for their detection. The bacterial virus MS2 is exceptional for its simplicity. MS2 is a 24nm icosahedral virus composed of only two proteins, 180 copies of coat protein(Mr=13.7KDa), a single copy of a maturation protein called A (Mr=44KDa) as well as a single stranded genomic RNA. As a result, it is a well characterized genetic and biochemical system (Golmoham madi et al., 1993;Konig et al., 2003;Ni et al., 1995;Stonehouse and Stockley, 1993;Stonehouse et al., 1996;Valegard et al., 1990;Valegard et al., 1991;Valegard et al., 1997;Valegard et al., 1986;van den Worm et al., 2006). Recently, our group has shown that the coat undergoes coat-specific changes in thickness during infection which we hypothesize are mediated by a single protein, A, using small angle scattering techniques in solution(Kuzmanovic et al., 2006b). Although, the change in thickness as measured by small angle neutron scattering (SANS) is dramatic, 21A to 31A in the absence A protein, these changes have not been observed previously using either cryo-EM or X-ray crystallography (Kuzmanovic et al., 2006b) (Golmohammadi et al., 1993;(Toropova et al., 2008)